This application is based upon and claims the benefit of priority under 35USC xc2xa7119 to Japanese Patent Application No. 2000-80442 filed on Mar. 22, 2000, No. 2000-208309 filed on Jul. 10, 2000, No. 2000-325727 filed on Oct. 25, 2000, and No. 2000-371825 filed on Dec. 6, 2000, the entire contents of which are incorporated by reference herein.
1. Field of the Invention
The present invention relates to displays for cellular phones, electronic books, etc. In particular, the present invention relates to a display having a digital memory for each display element and a method of driving such a display.
2. Description of the Related Art
Flat displays are becoming the mainstream of displays. Among the flat displays, liquid crystal displays (LCDs) are light, thin, and low-power-consumption, and therefore, are widely used for compact information terminals such as cellular phones and electronic books. These information terminals are usually driven by batteries, and due to this, reducing power consumption is a critical problem for them.
For example, the cellular phones are required to display images during a standby period at low power consumption. To achieve this, U.S. Pat. No. 5,712,652 discloses an image display having a memory cell (corresponding to a digital memory of the present specification) for each pixel. During a standby period (still-image display period), the image display activates only an AC driver for driving liquid crystals with alternating current and deactivates other peripheral drivers. This display is appropriate for displaying images involving no halftones at low power consumption. When applied to a cellular phone, this display shows images at low power consumption during a standby period.
Recent cellular phones have functions of displaying content from the Internet, or the images of the other ends of the phones. Images displayed during a data communication period (sometimes referred to as a xe2x80x9cnormal display periodxe2x80x9d herein) are usually full-color halftone images or moving images. Future cellular phones will have to be capable of not only operating at low power during a standby period but also displaying full-color, high-quality images during a data communication period.
The image display of U.S. Pat. No. 5,712,652 limits pixel voltage to two values. Due to this, the display is able to display an image with eight colors during a standby period but is unable to display full-color halftone images or moving images during a data communication period.
A conventional LCD with digital memories keeps still-image data in the digital memories when a still-image display period is switched to a normal display period. At the start of the next still-image display period, the still-image data stored in the digital memories is displayed until new still-image data is written into the digital memories. Namely, when a normal display period is switched to a still-image display period, a previous irrelevant image is momentarily displayed to provide a user with an unpleasant feeling or a disturbed image.
The LCD with digital memories alternately drives an entire display panel according to the output (or inverted output) of the digital memories, and therefore, load to drive during a still-image display period is extremely large compared with load to drive during a normal display period. This causes a voltage drop in a power source for the digital memories. If the digital memories supply video data stored therein to pixels before restoring the original potential thereof, a memory malfunction occurs to incorrectly display the video data. To prevent such a voltage drop, power source wires of the digital memories must have low resistance. To have low resistance, the power source wires must be widened on a substrate. This, however, increases pixel pitches and a frame area around a display panel of the LCD.
In addition, the power source wires of the digital memories increase the total number of wires on a substrate in the LCD, to enlarge pixel pitches, hinder high resolution, increase wire-to-wire short circuits, and deteriorate yield.
An object of the present invention is to provide a display, capable of displaying multicolor images at low power consumption during a standby period and full-color halftone images and moving images during a communication period, and a method of driving such a display.
Another object of the present invention is to provide a method of driving a display, capable of maintaining the quality of images when a still-image display period is switched to a normal display period.
Still another object of the present invention is to provide a display, capable of preventing a memory malfunction during a standby period, always displaying correct images, realizing high resolution, and reducing a frame area around a display panel.
Still another object of the present invention is to provide a display, capable of operating at low power and improving resolution and yield.
In order to accomplish the objects, a first aspect of the present invention provides a display having a first electrode substrate. The first electrode substrate has scan lines, data lines intersecting the scan lines, pixel electrodes formed at the intersections of the scan and data lines, respectively, and first switches provided for the pixel electrodes, respectively. Each first switch is turned on and off in response to a scan signal supplied from the scan line, and when turned on, electrically connects the data line to the pixel electrode so that video data from the data line is written into the pixel electrode. The display further has a second electrode substrate having common electrode that face the pixel electrodes with a predetermined gap between them, a display layer held between the first and second electrode substrates, a data driver for supplying video data to the data lines , and a scan driver for sequentially supplying a scan signal to the scan lines. The first electrode substrate has digital memories electrically connected to the pixel electrodes, respectively, and holding video data supplied from the data lines, and second switches each inserted between the corresponding pixel electrode and digital memory, to control conduction between the pixel electrode and the digital memory.
A second aspect of the present invention provides a display having a first electrode substrate. The first electrode substrate has scan lines, data lines intersecting the scan lines, pixel electrodes formed at the intersections of the scan and data lines, respectively, auxiliary capacitors electrically connected in parallel with the pixel electrodes, respectively, auxiliary capacitor lines for supplying a predetermined voltage to the auxiliary capacitors, first switches provided for the pixel electrodes, respectively, each first switch being turned on and off in response to a scan signal supplied from the corresponding scan line, and when turned on, writing video data from the corresponding data line into the corresponding pixel electrode, digital memories electrically connected to the pixel electrodes, respectively, and holding video data supplied from the data lines, and second switches each arranged between the corresponding pixel electrode and digital memory, to control conduction between the pixel electrode and the digital memory. The display further has a second electrode substrate having common electrode that face the pixel electrodes with a predetermined gap between them, and a display layer held between the first and second electrode substrates. The auxiliary capacitor lines also serve as power source lines for the digital memories.
A third aspect of the present invention provides a display having a first electrode substrate. The first electrode substrate has scan lines, data lines intersecting the scan lines, pixel electrodes formed at the intersections of the scan and data lines, respectively, auxiliary capacitors electrically connected in parallel with the pixel electrodes, respectively, auxiliary capacitor lines for supplying a predetermined voltage to the auxiliary capacitors, first switches provided for the pixel electrodes, respectively, each first switch being turned on and off in response to a scan signal supplied from the corresponding scan line, and when turned on, electrically connecting the corresponding data line to the corresponding pixel electrode so that video data from the data line is written into the pixel electrode, digital memories electrically connected to the pixel electrodes, respectively, and holding video data supplied from the data lines, second switches each arranged between the corresponding pixel electrode and digital memory, to control conduction between the pixel electrode and the digital memory, and memory control lines provided for the second switches, respectively, for supplying memory control signals to turn on and off the second switches. The display further has a second electrode substrate having common electrode that face the pixel electrodes with a predetermined gap between them, and a display layer held between the first and second electrode substrates. Potential controllers are connected between the second switches and the memory control lines, to control a rise of each memory control signal.
A fourth aspect of the present invention provides a display having a first electrode substrate. The first electrode substrate has scan lines, data lines intersecting the scan lines, pixel electrodes formed at the intersections of the scan and data lines, respectively, and first switches provided for the pixel electrodes, respectively, each first switch being turned on and off in response to a scan signal supplied from the corresponding scan line, and when turned on, electrically connecting the corresponding data line to the corresponding pixel electrode so that video data from the data line is written into the pixel electrode. The display further has a second electrode substrate having common electrode that face the pixel electrodes with a predetermined gap between them, a display layer held between the first and second electrode substrates, a data driver for supplying video data to the data lines at horizontal scan intervals, and a scan driver for sequentially supplying a scan signal to the scan lines at the horizontal scan intervals. During a first display period, the second switches are turned off to cut conduction between the pixel electrodes and the digital memories while the first switches are turned on at predetermined intervals to write video data from the data lines into the pixel electrodes and display the video data. In a second display period, the second switches are turned on to store video data from the data lines into the digital memories, and thereafter, the first switches are turned off to cut conduction between the data lines and the pixel electrodes, so that the video data stored in the digital memories is written into the pixel electrodes and is displayed.